[CSS Grid Layout] Fix grid shorthands CSSOM serialization

Source/core/css/StylePropertySerializer.h

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Research In Motion Limited. All rights reserved.
  * Copyright (C) 2013 Intel Corporation. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 28 matching lines @@
 
     String asText() const;
     String getPropertyValue(CSSPropertyID) const;
 private:
     String getCommonValue(const StylePropertyShorthand&) const;
     enum CommonValueMode { OmitUncommonValues, ReturnNullOnUncommonValues };
     String borderPropertyValue(CommonValueMode) const;
     String getLayeredShorthandValue(const StylePropertyShorthand&, bool checkShorthandAvailable = false) const;
     String get4Values(const StylePropertyShorthand&) const;
     String borderSpacingValue(const StylePropertyShorthand&) const;
-    String getShorthandValue(const StylePropertyShorthand&) const;
+    String getShorthandValue(const StylePropertyShorthand&, String separator = " ") const;
     String fontValue() const;
     void appendFontLonghandValueIfExplicit(CSSPropertyID, StringBuilder& result, String& value) const;
     String backgroundRepeatPropertyValue() const;
     String getPropertyText(CSSPropertyID, const String& value, bool isImportant, bool isNotFirstDecl) const;
     bool isPropertyShorthandAvailable(const StylePropertyShorthand&) const;
     bool shorthandHasOnlyInitialOrInheritedValue(const StylePropertyShorthand&) const;
     void appendBackgroundPropertyAsText(StringBuilder& result, unsigned& numDecls) const;
 
     // Only StylePropertySerializer uses the following two classes.
     class PropertyValueForSerializer {
@@ skipping 49 matching lines @@
         BitArray<numCSSProperties> m_longhandPropertyUsed;
         bool m_needToExpandAll;
     };
 
     const StylePropertySetForSerializer m_propertySet;
 };
 
 } // namespace blink
 
 #endif